Wikipedia:Reference desk/Archives/Science/2013 January 13

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

January 13

Polarization of light

Why partially polarized light produce glaring ? 106.209.16.55 (talk) 04:18, 13 January 2013 (UTC)

If I understand your question correctly, you've got it a little bit backwards: Partially polarized light doesn't produce glare. Rather, glare tends to be partially polarized. That's because it's reflected off of pavement, cement, the surface of water, et cetera, and those things differentially reflect incoming light of different polarization. That's why polaroid lenses are effective — they preferentially block the light that gets reflected from those surfaces, while passing the light polarized the other way. About half the light that you want to see is polarized the other way, so the brightness of the things you want to see is enhanced compared to that of the glare. --Trovatore (talk) 07:51, 13 January 2013 (UTC)

See section "Polarization by Scattering" of this. Here, it mentions Polarization by scattering is observed as light passes through our atmosphere. The scattered light often produces a glare in the skies. I want to know - Is there any relation between partially polarized light and glaring ? What means 'partially polarized light' ? 106.215.0.3 (talk) 10:49, 13 January 2013 (UTC)

See Brewster's angle. --catslash (talk) 01:40, 14 January 2013 (UTC)

What means 'partially polarized light' ? 106.196.135.149 (talk) 15:02, 14 January 2013 (UTC)

You may be interested in Polarized_light#In_nature_and_photography. Partially polarized light in this context essentially means that if light is separated into its components on some axis perpendicular to the direction of travel of the light (the components parallel to and perpendicular to this axis) as can be done for example using a polarizing filter, these two components are not equally bright. Fully polarized light has one of these components equal to zero on a suitably chosen axis. Unpolarized light has equal brightness on both axes, no matter what separation axis is chosen. The light going through a polarizing filter (you can use Polaroid sunglasses) is fully polarized. Experimenting with two sets of polarizing sunglasses, looking through both sets simultaneously while rotating one may help you understand this. — Quondum 16:05, 14 January 2013 (UTC)

Iron man

are all the technologies mention in the article currently possible? Or do we have to spend more money on research to get there? — Preceding unsigned comment added by 65.128.142.118 (talk) 07:40, 13 January 2013 (UTC)

Pretty much none of that technology exists. The prices are therefore completely fictional. Some things are just pure fantasy, such as the never-really-explained arc reactor and how the suit magically saves Tony from being squashed by extreme G-forces. Someguy1221 (talk) 08:42, 13 January 2013 (UTC)

At least a helmet with heads-up display is possible. StuRat (talk) 09:07, 13 January 2013 (UTC)

See [1]. A perfect recipe for Stark purée. Sagittarian Milky Way (talk) 10:35, 13 January 2013 (UTC)

Also see:

http://science.howstuffworks.com/transport/engines-equipment/jet-pack1.htm/printable (skip down to "Barriers to Jet Pack Development".

http://www.scientificamerican.com/article.cfm?id=rocket-pack&print=true

Guy Macon (talk) 19:22, 13 January 2013 (UTC)

As a scientifically-inclined critical thinker, when you read the linked article and try to decide if it is a reliable source, ask yourself which scenario is more likely: that a thorough analysis vetted by a team of experts actually studied the film's science and technology, and realistically estimated the feasibility and cost? Or, that this "news story" is a new media puff-piece designed as part of a "viral marketing" strategy for a Hollywood film franchise? Real, actual, forward-looking evaluations of future technology rarely takes the form of a quasi-advertisement. But, considering recent trends in marketing, this seems like a good way to put the movie franchise brand-name in front of a lot of eyeballs - they just have to produce content that's dissimilar enough from a conventional advertisement so as not to lose people's attention. The factual or scientific accuracy of the linked article is just credible enough - and no further - to maximize the estimated amount of exposure the piece attracts. And, you'll notice that the "research" was performed by an awfully spammy-looking website whose URL is plastered all over the "news article." This strategy is called traffic sharing; the "news article" was probably published in direct exchange for a fee from the advertiser(s) and their traffic network. Nimur (talk) 02:28, 14 January 2013 (UTC)

Tuatara - a third eye in humans too?

Having recently seen my first tuatara, the New Zealand reptile with a third eye on the top of its head, it has set me wondering about the many religions eg. Hinduism, which claim a third eye for humans,somewhere between the eyebrows or on the forehead. Has anyone ever found please, the remotest trace of such an eye in any species rather more closely related to me than the tuatara? With thanks. — Preceding unsigned comment added by 109.12.63.220 (talk) 10:58, 13 January 2013 (UTC)

The relevant articles are at parietal eye (the biological concept) and third eye (the mystical concept). The two are not related, so far as I can tell. Matt Deres (talk) 14:23, 13 January 2013 (UTC)

It's curious whether any of the Eastern religions depict the third eye in any animals that have one. μηδείς (talk) 16:57, 13 January 2013 (UTC)

Matt Deres -- Madame Blavatsky connected the two in Theosophy in the late 19th century... AnonMoos (talk) 13:36, 14 January 2013 (UTC)

[2] gives an interesting history of the pineal and the fascination of Rene Descartes and others with it. Surprisingly, at least in that review, the first connection with the "third eye" is only in 1828! Though I wouldn't rule out that clever ancients might have had a notion of it anyway... Wnt (talk) 04:38, 15 January 2013 (UTC)

DNA Testing

Is it possible to take a DNA sample from an unborn foetus with a cotton bud, in order to establish paternity without harming the developing child? --Andrew 18:50, 13 January 2013 (UTC)

How are you proposing to bring a cotton bud into contact with an unborn child? AlexTiefling (talk) 18:55, 13 January 2013 (UTC)

There are more ways of sampling DNA than using a cotton bud. If one were to attempt to sample foetal DNA, one method would be amniocentesis. This gets cells from the fluid surrounding the foetus, without contacting the foetus directly. It involves needles and some small risk to the foetus, so it's certainly not a "do at home" procedure. Another option, as there typically is transfer of foetal cells into the mother's bloodstream, is to do a blood draw of the mother, and then separate out the foetal cells from the mother's cells. Less risk to the foetus, but more complicated to work up. - Long story short, any sort of prenatal genetic testing is going to require the involvement of a licensed doctor to do the sampling, and probably involves expense and risks that likely wouldn't be justified just for paternity testing. Most doctors would probably recommend simply waiting several months until the kid is born. -- 71.35.120.28 (talk) 19:13, 13 January 2013 (UTC)

Unless, of course, the goal is to decide whether to have an abortion based on paternity. This raises ethical questions that I do NOT think should be discussed here at the reference desk. --Guy Macon (talk) 19:27, 13 January 2013 (UTC)

• We don't want an abortion, we just want a lack of ambiguity and no surprises =]. Thanks for all of the helpful information --Andrew 19:33, 13 January 2013 (UTC)

Then you should wait. Amniocentesis includes a risk to the fetus which is not justified absent other factors. It is not a routine test and should not be performed unless the data gathered from it will determine a course of action. Paternity that won't be used in an abortion decision is not a reason to risk the baby. --DHeyward (talk) 05:55, 14 January 2013 (UTC)

Ultrasound imaging will tell you the sex of the foetus well before its' born. It has a low level of risk but is in most developed countries pretty standard for detecting abnormallities and abnormal positioning. Wickwack 121.215.4.48 (talk) 00:17, 14 January 2013 (UTC)

If you google "prenatal paternity test" you can find companies that specialize in that, at least one of which only requires a blood sample from the mother and alleged father. The less-invasive method that only requires a blood test costs about $1000, though, about twice the price of a test using amniocentesis. Red Act (talk) 01:26, 14 January 2013 (UTC)

I would urge strong caution with such tests. [3] is somewhat old now for what's likely a fairly rapidly evolving field but is still a decent read. A key point is there seems to have been limited research published in per reviewed articles on these testing services. (As our Prenatal diagnosis suggests, most more serious research is in attempts to detect chromosomal and genetic abnormalities.) I also remember when Baby Gender Mentor was on the main page as the FA, it was a while ago but the article said then (although there was some criticism it didn't go far enough and it was eventually delisted as a FA) as it does now that even for this far easier test the reliability was questioned. Prenatal sex discernment mentions recent (2011) research suggesting that the sort of thing is reasonably reliably by now (98%) but prenatal paternity testing is still in more of an infancy stage. Since the OP is not considering anything drastic the risks of it being wrong may be lower, but they still may want to consider whether there's any point getting a test which may cause unnecessary ill feeling, stress etc from a result which could easily be wrong. At the very least, I would recommend all involved parties see a professional for advice Nil Einne (talk) 11:27, 14 January 2013 (UTC)

Not everyone lives in a country where you'll be charged for an amniocentesis! Here in the UK amniocentesis will be offered free of charge on the NHS if the early ultrasounds determine that the child is at an increased risk of Down syndrome or (less probably - both in terms of incidence and likelihood of early detection) a range of other chromosomal aneuploidies. The test can be used for complete DNA fingerprinting, but this isn't usually done. The procedure carries an approximately 1/200 chance of causing a miscarriage, which is why it's only used if the scan indicates it's relevant. I still have no clue how the OP thinks his partner's body is configured, that a cotton bud was going to be a feasible sampling method. AlexTiefling (talk) 15:32, 14 January 2013 (UTC)

20 years ago, the NHS gave us a free amniocentesis in order to check for Down syndrome purely because of my wife's age (late-thirties at the time). It was not a clear-cut decision to do that test though - there is a significant risk of harming the baby - so unless the risk of the thing you're testing for outweighs the risk from the procedure, no ethical doctor would perform the procedure. However, even if you needed an amnio, I don't know whether they'd provide paternity testing on the basis of the DNA that results of that. The did tell us the sex of the baby - but as has been pointed out, modern ultrasound machines can show that quite easily. But the OP's idea that you could somehow use a cotton bud to collect the unborn child's DNA shows a profound lack of knowledge of the biology/geometry of the womb during pregnancy! The answer to the original question is a definite "NO!". SteveBaker (talk) 17:34, 14 January 2013 (UTC)

It is at least theoretically possible to determine the paternity of a fetus at 5-12 weeks of gestation, because Y chromosomal sequences can be pulled out of the mother. [4][5] The same test could be done with specific X chromosomal sequences from the father in the case of a girl (or with any other paternal sequences as long as both chromosomes are checked for). However, there is some risk of confusion with cells lingering on from a prior pregnancy.[6] (During the Monica Lewinsky situation I was amused to note that the paternity of the abortion might have been determined by this means, but no doubt it was for the best that some Republicans were behind on their tech). Wnt (talk) 00:58, 15 January 2013 (UTC)

Tellurium suboxide = tellurium monoxide?

Hi. I've been trying to write an article on tellurium suboxide (which I've read is used in CD-RW disks), but the only sources I can find for the compound's chemical information call it tellurium monoxide, which has the same formula as tellurium suboxide. Are the two compounds the same? Thanks

^King Jakob _C 20:48, 13 January 2013 (UTC)

No, tellurium monoxide (TeO) is a tellurium suboxide, but a tellurium suboxide is not necessarily TeO. Tellurium suboxide is not a single compound, but comprises all tellurium-oxygen compounds that have relatively less than two oxygen atoms per tellurium atom (because the 'normal' oxide of tellurium is TeO₂). See this website: tellurium suboxide is TeO_x, where 0<x<2. This means that TeO is a tellurium suboxide, but Te₂O₃ or Te₄O₂ are also tellurium suboxides (I don't know if these actually exist, but there are many other possibilities). - Lindert (talk) 22:24, 13 January 2013 (UTC)

OK, thanks. ^King Jakob _C 22:28, 13 January 2013 (UTC)

Wait, do you know which tellurium suboxide is used in CD-RW disks? ^King Jakob _C 22:38, 13 January 2013 (UTC)

I suspect it's a mixture of different compounds, but don't take my word for it (I'm not even a chemist). This abstract, which is about optical memory, mentions using TeO_x with x varying between 0.8 and 1.2, and this paper talks about x=1 (so it could be simply TeO). Maybe someone with more knowledge of this subject can help out? - Lindert (talk) 23:05, 13 January 2013 (UTC)

I have some experience with producing various kinds of RW disks. The company I worked with used a AgInSbTe (silver-indium-antimony-tellurium) quaternary alloy with 5% Ag, 9% In, 57% Sb and 29% Te. One of our competitors bumped up the Sb and reduced everything else, and we speculated that their formulation had something to do with them using a different kind of dielectric layer. I have heard that some manufacturers use GeInSbTe. This was a number of years ago, so the preferred material may have changed since then. You might also want to look at GeSbTe.

http://books.google.com/books?id=AO3SNSM2ykUC&pg=PA219&lpg=PA219&dq=rewritable+optical+GeInSbTe&source=bl&ots=GAVyNUHfqN&sig=72FKOoWjwjxgC2yEqxtGf8v2GWs&hl=en

and

http://www.phy.bme.hu/Kristalyos_es_amorf_anyagok/0387848738_Materia.pdf

gives more of a chemists viewpoint rather than my engineering viewpoint. --Guy Macon (talk) 07:10, 14 January 2013 (UTC)